Aqueous dispersion compositions containing a polytetrafluoroethylene [PTFE] resin have so far been used for producing impregnated articles, such as roofing materials for membrane structures, by impregnating glass fibers, carbon fibers, Kevlar fibers and the like therewith and, further, for forming films by applying them to articles to be coated, or substrates, followed by baking, in such application fields as high-frequency printed circuit boards, conveyor belts and packing materials.
The conventional PTFE resin-containing aqueous dispersion compositions have a problem in that when they undergo mechanical stresses, PTFE particles readily coagulate, possibly resulting in deteriorations in the quality of the compositions or films or impregnated articles obtained by using them. Thus, when such compositions are transported using a pump or the like, agglomerates may be formed in the compositions, possibly leading to pump inside or filter blocking. Further, on the occasion of application thereof to metal substrates or fibrous substrates using a doctor bar to form coatings uniform in thickness, agglomerates may be formed in the vicinity of the doctor bar and remain as foreign matters on the coatings. On the occasion of forming coatings on various substrates therefrom using a spray gun, agglomerates may be formed in the nozzle portion of the gun and adhere as foreign matters onto the coatings.
For improving such mechanical stability, a PTFE-containing aqueous dispersion composition has been proposed which contains polyethylene oxide or a water-soluble polyurethane-based associated type thickening agent or viscosity increasing agent as incorporated therein (cf. e.g. Patent Document 1: Japanese Kokai (Laid-open) Publication 2000-198899 (Claim 1, [0019])).
However, Patent Document 1 does not describe any PTFE-containing aqueous dispersion composition containing a water-soluble high-molecular compound other than polyethylene oxide or a water-soluble polyurethane-based associated type thickening agent as incorporated therein.